“He makes a whole different kind of ‘America’ visible behind the obvious, contemporary one,” the film director Wim Wenders has said of Sam Shepard. And who would disagree? Shepard is perhaps the most uncomfortable of America's giant playwrights. He takes few prisoners in a mythic landscape of desperate cowboys, domestic mayhem and a frontier, Wild West turned gothic by internal, psychic disturbance.

Chill winds blow through Shepard territory. And The God of Hell is no exception. But this time, it's external. Kathy Burke's hard-driving Donmar production ends with a mid-west moan echoing through the audience, emblematic of the condition Shepard evidently feels his country to be in.

Something is rotten in the state and in The God of Hell, first premiered last year in New York, Shepard doesn't mince his words or his images. “We're in absolute command now,” yells Ben Daniels' mesmerising government henchman, Welch. “No more of that nonsense of checks and balances...all that hanging around in limbo, waiting for decisions from committees and tired-out lobbies.”

By a long chalk, The God of Hell is certainly not Shepard's best – hardly comparable with Fool for Love, True West or even Matthew Warchus' magnificent revival of Buried Child last year for the NT. By comparison, this new play feels like a crude slab of anti-government propaganda. Which is to say, this is Shepard, the undiminished, counter-culture radical in full flow, giving us a warning (as much environmental in the cause of small farmers as political) in a setting caught between everyday realism (terrific American interior from Jonathan Fensom) and the plainly surreal.

Frank (Stuart McQuarrie), a docile dairy farmer and Emma (a surprisingly winsome Lesley Sharp) are living quiet domestic lives on their Wisconsin farm when they are visited by two strangers – Welch and a friend of Franks, Haynes – a scared, paranoid-fuelled Ewen Bremner. He's red hot, so red hot, if you touch him, sparks literally fly.

Like Pinter's The Birthday Party (with which it shares definite similarities), unnamed terrors and unanswered questions hang in the air: the reasons for Haynes' institutionalised torture, his plutonium contaminated (the god of hell of the title) state. A little local leakage perhaps?

Suffice it to say, lives are overturned forever and Shepard's disgust with officialdom emerges as something close to a grotesque parable and twice as damning. American Democracy never looked so shaky. Ignore at your peril.

- Carole Woddis